The HP Indigo line of digital printing presses is based on digital offset color technology, which combines ink-on-paper quality with multi-color printing on a wide range of paper, foil and plastic substrates. These digital printing presses offer cost-effective short-run printing, on-demand service and on-the-fly color switching.
A digital offset printing system works by using digitally controlled lasers to create a latent image in the charged surface of a photo imaging plate (PIP). The lasers are controlled according to digital instructions from a digital image file. Digital instructions typically include one or more of the following parameters: image color, image spacing, image intensity, order of the color layers, etc. Special ink is then applied to the partially-charged surface of the PIP, recreating the desired image. The image is then transferred from the PIP to a heated blanket cylinder, and from the blanket cylinder to the desired substrate, which is placed into contact with the blanket cylinder by means of an impression cylinder. The ink is fluid on the heated blanket. Because of its role in transferring an image from the PIP to the ultimate substrate, the blanket may sometimes be referred to as an “intermediate transfer member” (ITM).
A detailed description of the operation of a typical digital offset printer is described in Hewlett-Packard (HP) White Paper Publication, “Digital Offset Color vs. Xerography and Lithography”, for example. Specifically, an example of a digital printer that can be used to create the disclosed printed articles is HP's digital printing press Indigo Press™. 1000, 2000, 4000, or newer, presses, manufactured by and commercially available from Hewlett-Packard Company of Palo Alto, Calif., USA.
In order to apply pressure evenly in the course of transferring the ink and to accommodate slight variations in the surface of the substrate, the blanket is typically formed from a resilient material, such as synthetic rubber. Silicone is usually preferred, however, for the outermost layer of the blanket, because of its exceptional ink release properties. Such a silicone layer is an example of a release layer known in the art.
It is difficult to apply a silicone release layer on a rubber underlayer, however, because the desirable release properties of silicone and the properties of rubber also make it difficult to form chemical bonds at their respective surfaces. Known methods include applying a primer layer on the rubber, waiting for the primer to dry, or curing the primer, before then applying the silicone release layer. This is time-consuming and not an efficient method of manufacture.
Moreover, when forming a silicone release layer using for example a platinum catalyst in an addition-cure reaction, compounds from the underlying rubber layer or the body of the blanket cylinder under the blanket can inhibit or stop the curing reaction, by poisoning the catalyst. This is detrimental to the quality of the resulting silicone release layer.